Novel low viscosity functional fluid composition

ABSTRACT

A low viscosity functional fluid composition or brake fluid, exhibiting a dry equilibrium reflux boiling point (ERBP) of at least 260° C. and/or a wet equilibrium reflux boiling point (WERBP) of at least 180° C., comprising
         (A) from 15 to 90% of alkoxy glycol borate esters [R 1 —O—(CH 2 CH 2 —O) n ] 3 B, wherein R 1  is a C 1 - to C 8 -alkyl radical and n has a value of from 2 to 6,   (B) from 5 to 80% of alkoxy glycol components R 2 —O—(CH 2 CH 2 —O) m —H, wherein R 2  is a C 1 - to C 8 -alkyl radical and m has a value of from 2 to 6,   (C) from 0.1 to 10% of an additive package comprising additives with corrosion inhibition action, wherein at least one of the additives contained in the additive package is selected from alkylamine ethoxylates.

The present invention relates to a low viscosity functional fluid composition comprising

-   -   (A) from 15 to 90% by weight, based on the weight of the total         composition, of one or more alkoxy glycol borate esters having         the general formula (I)

[R¹—O—(CH₂CH₂—O)_(n)]₃B  (I)

-   -    wherein R¹ is a C₁- to C₄-alkyl radical or a mixture of such         radicals and n has a value of from 2 to 6,     -   (B) from 5 to 80% by weight, based on the weight of the total         composition, of one or more alkoxy glycol components having the         general formula (II)

R²—O—(CH₂CH₂—O)_(m)—H  (II)

-   -    wherein R² is a C₁- to C₈-alkyl radical or a mixture of such         radicals and m has a value of from 2 to 6, R² and/or m being         different or identical to R¹ and/or n, respectively,     -   (C) from 0.1 to 10% by weight, based on the total weight of the         composition, of an additive package comprising one or more         additives with corrosion inhibition action, wherein at least one         of the additives contained in the additive package of         component (C) is selected from alkylamine ethoxylates.

The said low viscosity functional fluid composition is useful in a variety of applications and in particular as a brake fluid, especially for new electronic or automated anti-lock brake systems which require lower viscosity fluids for satisfactory operation at low temperatures.

Functional fluid compositions based on borate esters are well known in the art. To be usefuel for example as DOT 4 or DOT 5.1 brake fluids, these borate ester based compositions must meet stringent physical properties and performance requirements particularly with respect to minimum dry equilibrium reflux boiling point (“ERBP”), minimum wet equilibrium reflux boiling point (“WERBP”) and maximum low temperature kinematic viscosity (e.g. determined at —40° C.) while maintaining adequate resistance to corrosion, stability and meeting other physical property requirements such as pH, reserve alkalinity and rubber swell.

WO 00/65001 describes hydraulic fluids comprising alkoxy glycol borate esters, alkoxy glycols and corrosions inhibitors, further containing cyclic carboxylic acid derivatives.

WO 02/38711 describes low viscosity functional fluid compositions comprising alkoxy glycol borate esters, alkoxy glycol components and additives such as corrosion inhibitors, wherein the alkoxylation degrees of the alkoxy glycol borate esters and the alkoxy glycols are restricted to a certain narrow pattern.

There is a strong demand for improved high performance hydraulic fluid compositions and brake fluids having low temperature viscosity while meeting or exceeding at the same time the minimum ERBP and especially the WERBP temperature requirements as fulfilled by the hydraulic fluid compositions and brake fluids described in the art.

According to the present invention, the above-defined functional fluid composition has been found which exhibits superior values of ERBP and of WERBP and for low temperature kinematic viscosity while maintaining excellent resistance to corrosion, high stability and meeting other physical property requirements such as pH, reserve alkalinity and rubber swell. Especially very high WERBP values are achieved. Moreover, kinematic viscosity value at very low temperatures below −40° C., e.g. at −50° C., are superior compared to functional fluid compositions of the art.

The alkylamine ethoxylates as part of component (C) and their interaction with the other components and additives of the present functional fluid composition are deemed to be responsible for the superior performance and especially for the very high WERBP values.

The alkylamine residue in the said alkylamine ethoxylates may be a secondary or preferably a primary aliphatic monoamine which is capable of being ethoxylated. Usually secondary or preferably primary aliphatic monoamines are used, however, polyamines with with at least one secondary and/or primary amino group which is capable of being ethoxylated may also be used. The alkyl residues to the nitrogen atom normally comprise saturated linear or branched alkyl groups, however, unsaturated linear or branched alkyl residues or saturated or unsaturated cycloalkyl residues may also be comprised by the term “alkyl”.

In a preferred embodiment, the said alkylamine ethoxylates comprise at least one linear or branched C₃ to C₂₀ alkyl chain, preferably at least one linear or branched C₆ to C₁₃ alkyl chain, more preferably at least one linear or branched C₇ to C₁₂ alkyl chain, most preferably at least one linear or branched C₈ to C₁₁ alkyl chain. Preferably, the term “alkyl chain” here means saturated and non-cyclic hydrocarbon residues. The alkylamine ethoxylates may also comprise mixtures of such alkyl chains, for example a mixture of homologue alkyl residues, depending on the specific technical or natural origin of the alkylamines used.

Suitable examples for single alkylamine molecules being capable for ethoxylation and, therefore, suitable as surfactants for the instant invention are n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, n-pentylamine, tert-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, 2-ethylhexylamine, n-nonylamine, n-decylamine, 2-propylheptylamine, n-undecylamine, n-dodecylamine, n-tridecylamine, isotridecylamine, n-tetradecylamine, n-pentadecylamine, n-hexadecylamine, n-heptadecylamine, n-octadecylamine, n-nonadecylamine, n-eicosylamine, di-(n-hexyl)amine, di-(n-heptyl)amine, di-(n-octyl)amine, di-(2-ethylhexyl)amine, di-(n-nonyl)amine, di-(n-decyl)amine, di-(2-propylheptyl)amine, di-(n-undecyl)amine, di-(n-dodecyl)amine, di-(n-tridecyl)amine, di-(isotridecyl)amine, di-(n-tetradecyl)amine, di-(n-pentadecyl)amine, di-(n-hexadecyl)amine, di-(n-heptadecyl)amine, di-(n-octadecyl)amine, di-(n-nonadecyl)amine, di-(n-eicosyl)amine, n-hexylmethylamine, n-heptylmethylamine, n-octylmethylamine, (2-ethylhexyl)methylamine, n-nonylmethylamine, n-decylmethylamine, (2-propylheptyl)methylamine, n-undecylmethylamine, n-dodecylmethylamine, n-tridecylmethylamine, isotridecylmethylamine, n-tetradecylmethylamine, n-pentadecylmethylamine, n-hexadecylmethylamine, n-heptadecylmethylamine, n-octadecylmethylamine, n-nonadecylmethylamine and n-eicosylmethylamine.

Such alkyl residues may be derived entirely from petrochemical production, for example technical C₈-C₁₅ alkyl mixtures, 2-ethylhexyl or 2-propylheptyl, or may entirely or partially be based on renewable raw materials, for example fatty amines such as stearyl amine, oleyl amine or tallow amine may be used as the basis for the alkylamine ethoxylates.

The degree of ethoxylation is usually from 1 to 35 EO units per alkylamine molecule, i.e. the at least on alkylamine ethoxylate comprises from 1 to 35 EO units, preferably from 1.5 to 15 EO units, more preferable from 1.8 to 9 EO units, most preferably from 2 to 6 EO units. The said ethoxylation degree is a statistical value, i.e the alkylamine ethoxylates have normally to be regardes as mixtures of species (homologues) with different numbers of EO units.

In an especially preferred embodiment of the instant invention, the at least one alkylamine ethoxylate comprises at least on linear C₃ to C₂₀ alkyl chain and from 1 to 35 EO units; more preferably the at least one alkylamine ethoxylate comprises at least on linear C₆ to C₁₃ alkyl chain and from 1.5 to 15 EO units; most preferably the at least one alkylamine ethoxylate comprises at least one linear C₇ to C₁₂ alkyl chain and from 1.8 to 9 EO units, especially the at least one alkylamine ethoxylate comprises at least one linear C₈ to C₁₁ alkyl chain and from 2 to 6 EO units.

Such alkylamine ethoxylates may be primary amines with one oxyethylene chain of general formula Alkyl-NH—(CH₂CH₂O)_(m)—H or primary amines with two oxyethylene chains of general formula Alkyl-N[(CH₂CH₂O)_(p)'H][(CH₂CH₂O)_(q)—H] or secondary amines of general formula (Alkyl)₂N—(CH₂CH₂O)_(m)—H or mixtures of such primary amines with one oxyethylene chain and such primary amines with two oxyethylene chains or mixtures of such primary and secondary amines, wherein m and (p+q), respectively, are the total ethoxylation degrees. “Alkyl” in the above formulas normally means C₃ to C₂₀ alkyl, preferably C₆ to C₁₃ alkyl, more preferably C₇ to C₁₂ alkyl, most preferably C₈ to C₁₁ alkyl, as defined above. Residual alkylamine species may also be present in lower amounts, especially with low total ethoxylation degrees below 2.

A typical suitable alkylamine ethoxylate is octylamine (caprylamine) with 2 EO units which is commercially available.

The said alkylamine ethoxylates can be prepared by usual methods such as the reaction of the alkylamine with ethylene oxide under catalysis by alkali metal hydroxides or under catalysis by double metal cyanides, as known to the skilled person in the art.

The said alkylamine ethoxylates has partly corrosion inhibition properties and partly solvent properties for the functional fluid composition or brake fluid, respectively, according to the present invention.

Component (A) of the functional fluid composition of general formula (I) comprises species of ethoxylation degree of from n=2 to n=6, preferably of from n=2 to n=4, more preferably of n=3. Component (A) may be a single species or a mixture of different species with regard to the ethoxylation degree and/or to radical R¹. Radical R¹ is preferably a C₁- to C₄-alkyl radical and may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl and 2-ethylhexyl, ethyl and especially methyl being preferred.

The said borate esters and their methods of preparation are well known in the art. Borate esters especially useful in the functional fluid composition of the present invention may be prepared by reacting boric acid with suitable alkoxy glycol components which are different or identical to those of component (B). Typically, such alkoxy glycol components are mixtures of different species with regard to the ethoxylation degree and/or to radical R¹.

Examples of useful borate esters include those containing methyl triethylene glycol borate ester which can also be named tris-[2-[2-(2-methoxyethoxy)-ethoxy]-ethyl)orthoborate, ethyl triethylene glycol borate ester, n-butyl triethylene glycol borate ester and mixtures thereof. Further useful borate esters include those containing methyl tetraethylene glycol borate ester, methyl diethylene glycol borate ester, ethyl tetraethylene glycol borate ester, ethyl diethylene glycol borate ester, n-butyl tetraethylene glycol borate ester, n-butyl diethylene glycol borate ester and mixtures thereof.

In a preferred embodiment, component (A) comprises at least on alkoxy glycol borate ester of general formula (I) wherein the ethoxylation degree has a value of n=3 and R¹ is a methyl radical.

Component (B) of the functional fluid composition of general formula (II) comprises species of ethoxylation degree of from m=2 to m=6, preferably of from m=2 to m=4. Component (B) may be a single species or a mixture of different species with regard to the ethoxylation degree and/or to radical R². Radical R² is preferably a C₁- to C₄-alkyl radical and may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl and 2-ethylhexyl, ethyl and especially methyl being preferred.

Examples of useful alkoxy glycols for component (B) of the present invention include methyldiglycol, methyltriglycol, methyltetraglycol, methylpentaglycol, methylhexaglycol, ethyldiglycol, ethyltriglycol, ethyltetraglycol, ethylpentaglycol, ethylhexaglycol, n-propyldiglycol, n-propyltriglycol, n-propyltetraglycol, n-propylpentaglycol, n-propylhexaglycol, n-butyldiglycol, n-butyltriglycol, n-butyltetraglycol, n-butylpentaglycol, n-butylhexaglycol, n-pentyldiglycol, n-pentyltriglycol, n-pentyltetraglycol, n-pentylpentaglycol, n-pentylhexaglycol, n-hexyldiglycol, n-hexyltriglycol, n-hexyltetraglycol, n-hexylpentaglycol, n-hexylhexaglycol, 2-ethylhexyldiglycol, 2-ethylhexyltriglycol, 2-ethylhexyltetraglycol, 2-ethylhexylpentaglycol, 2-ethylhexylhexaglycol and mixtures thereof. For the avoidance of doubt, “glycol” always means “ethylene glycol”.

In a preferred embodiment, component (B) comprises a mixture of alkoxy glycols of general formula (II) comprising solely or predominantly species with m=3. Predominantly shall mean that at least 60% by weight, more preferably at least 75% by weight, most preferably at least 90% by weight, of component (B) comprises species with m=3. In the last case, alkoxy glycol species with m=2 and/or m=4 and/or m=5 and/or m=6 may be present in minor amounts.

A preferred mixture of such alkoxy glycols for component (B) with m=3 is a mixture consisting solely or essentially of methyltriglycol and n-butyltriglycol. Typically, the weight ratio of methyltriglycol to n-butyltriglycol in this mixture is from 5:1 to 1:2, especially from 2:1 to 1:1.

Component (C) of the present functional fluid composition may comprise, besides the alkylamine ethoxylates, at least one additive with corrosion inhibition action, although the alkylamine ethoxylates exhibit corrosion inhibition properties themselves. Suitable customary additives with corrosion inhibition properties include fatty acids such as lauric, palmitic, stearic or oleic acid; esters of phosphorus or phosphoric acid with aliphatic alcohols; phosphites such as ethyl phosphate, dimethyl phosphate, isopropyl phosphate, n-butyl phosphate, triphenyl phosphite and diisopropyl phosphite; heterocyclic nitrogen containing organic compounds such as benzotriazole, tolutriazole, 1,2,4-triazole, benzoimidazole, purine, adenine and derivatives of such heterocyclic organic compounds; alkylamines such as mono- and di-(C₄- to C₂₀-alkyl)amines, e.g. n-butylamine, n-hexylamine, n-octylamine, 2-ethylhexylamine, isononylamine, n-decylamine, n-dodecylamine, oleylamine, d-n-proylamine, di-isopropylamine, di-ni-butylamine, di-n-amylamine, cyclohexylamine and salts of such alkylamines; alkanolamines such as mono-, di- and trimethanolamine, mono-, di- and triethanolamine, mono-, di- and tri-n-propanolamine and mono-, di- and tri-isopropanolamine. Of course, mixtures of the above additives with corrosion inhibition action can be used.

Using alkylamines and/or alkanolamines as compounds with corrosion inhibition action in the additive package of component (C) often results in an additional decrease in viscosity of the present functional fluid composition.

Besides the alkylamine ethoxylates and possibly the additives with corrosion inhibition action, further customary additives may be present in the additive package of component (C), for example stabilizers such as pH stabilizers, antioxidants such as phenolthiazine and phenolic compounds, e.g. hydroxyanisol and bisphenol A, defoamers and dyes.

Preferably, the additive package of component (C) which includes one or more alkylamine ethoxylates consists or consists essentially of a major portion of additives with corrosion inhibition action and a minor portion of additives with antioxidant action and possibly of defoamers and dyes. The portion of alkylamine ethoxylate(s) in the additive package of component (C) is typically of from 1 to 100% by weight, preferably of from 10 to 99% by weight, more preferably of from 25 to 98% by weight, most preferably of from 40 to 97% by weight, each based on the weight of the additive package of component (C).

It is contemplated that also other materials than components (A), (B) and (C) may be formulated into the present functional fluid composition so long as care is taken not to lower the ERBP or WERBP temperatures below the superior high levels of the instant invention or to increase the low temperature viscosity above an acceptable level. For example, the present functional fluid composition may include from 0 to 20% by weight, based on the total weight of the composition, of a diluent or a lubricant such as, for example, polyethylene oxides, polypropylene oxides, poly(C₄- to C₁₀-alkylene) oxides, dialkoxyglycols or borate co-esters.

According to the present invention, the three components (A), (B) and (C) are present in the functional fluid composition in the following amouts:

-   -   (A) from 15 to 90% by weight, preferably from 30 to 75% by         weight, more preferably from 45 to 65% by weight, most         preferably from 56 to 62% by weight;     -   (B) from 5 to 80% by weight, preferably from 20 to 65% by         weight, more preferably from 32 to 52% by weight, most         preferably from 36 to 42% by weight;     -   (C) from 0.1 to 10% by weight, preferably from 0.5 to 7% by         weight, more preferably from 1 to 4% by weight, most preferably         from 1.5 to 2.5% by weight.

All % values for (A), (B) and (C) above refer to the total composition of the present functional fluid composition, or—if other materials than components (A), (B) and (C), e.g. the above-mentioned diluents and/or lubricants, are present—to the total weight of (A) plus (B) plus (C). The % values for (A), (B) and (C) add up in each case to 100% by weight.

The functional fluid composition of the present invention exhibits superior behavior in ERBP and WERBP temperature and simultaneously in low temperature viscosity performance. Preferably, it exhibits a ERBP of at least 260° C., more preferably of at least 265° C., most preferably of at least 270° C., and/or a WERBP of at least 180° C., more preferably of at least 182° C., still more preferably of at least 184° C., most preferably of at least 187° C.

The functional fluid composition of the present invention exhibits a low temperature kinematic viscosity of preferably less than 700 centistokes (“cSt”) (=mm²/s), more preferably of less than 685 cSt, most preferably less than 675 cSt, each determined at a temperature of −40° C.

The functional fluid composition of the present invention exhibits a low temperature kinematic viscosity of preferably less than 4000 cSt, more preferably of less than 3000 cSt, most preferably less than 2600 cSt, each determined at a temperature of −50° C., whereas typical functional fluid compositions of the art exhibit low temperature kinematic viscosities in the region from about 4500 cSt to about 6000 cSt at −50° C.

The low viscosity functional fluid composition of the present invention is especially useful as a brake fluid, for example for vehicles such as passenger cars and trucks, especially for new electronic or automated anti-lock brake systems which require lower viscosity fluids for satisfactory operation at low temperatures.

Besides its superior behavior in ERBP and WERBP temperature and its low temperature viscosity performance, the functional fluid composition of the present invention exhibits a good corrosion protection, a good water compatibility, a mild pH value, a good stability with regard to low and high temperatures, a good oxidation stability, a good chemical stability, a good behavior towards rubber and elastomers and a good lubrication performance.

The following examples are intended to demonstrate the behavior and performance of the low temperature functional fluid composition of the present invention without limiting it.

EXAMPLES

The ERBP and WERBP temperatures and kinematic viscosity values of the following function fluid compositions according to the present invention (“FFC1” and “FFC2”) were determined according to test procedures described in Department of Transportation Standard FMVSS 116 (corresponding to SAE J 1704). For comparision, the corresponding values of Example 8 of WO 02/38711 (“FFC3”), which is the example with the highest WERPB (i.e. 186° C.) in this document the values therefor having also been determined according to FMVSS 116, are confronted to FFC1 and FFC2.

Compositions of FFC1, FFC2 and FFC3 [% by weight]:

FFC1 FFC2 FFC3 Methyl triethylene glycol borate ester 61.00 61.00 61.00 Methyl triethylene glycol 20.00 20.00 30.50 n-Butyl triethylene glycol 17.345 17.145 2.00 Ethyl triethylene glycol 0 0 2.50 Hexyl diethylene glycol 0 0 2.00 Diisopropanolamine 0 1.00 2.00 Octylamine ethoxylate (2 EO units) 1.60 0.80 0 Tolutriazol 0.05 0.05 0 Ester of phosphoric acid 0.005 0.005 0

ERBP, WERBP and kinematic viscosity of FFC1, FFC2 and FFC3:

kinematic viscosity ERBP [° C.] WERBP [° C.] (−40° C.) [cSt] FCC1 277 189 659 FCC2 274 188 670 For comparison: FCC3 265 186 681 FCC2 kinematic viscosity (−50° C.) 2523 [cSt]: 

1. A functional fluid composition comprising: from 15 to 90% by weight, based on a weight of a total composition, of an alkoxy glycol borate ester of formula (I) [R¹—O—(CH₂CH₂—O)_(n)]₃B  (I)  wherein R¹ is a C₁- to C₈-alkyl radical or a mixture of such radicals and n has a value of from 2 to 6, from 5 to 80% by weight, based on the weight of the total composition, of an alkoxy glycol component of formula (II) R²—O—(CH₂CH₂—O)_(m)—H  (II)  wherein R² is a C₁- to C₈-alkyl radical or a mixture of such radicals, and m has a value of from 2 to 6, from 0.1 to 10% by weight, based on the total weight of the composition, of an additive package comprising an additive having corrosion inhibition action, wherein the additive is selected from alkylamine ethoxylates.
 2. The functional fluid composition according to claim 1, wherein the alkylamine ethoxylate comprises at least one C₃ to C₂₀ alkyl chain.
 3. The functional fluid composition according to claim 1, wherein the alkylamine ethoxylate comprises from 1 to 35 ethylene oxide units.
 4. The functional fluid composition according to claim 1, wherein the alkylamine ethoxylate comprises a linear C₇ to C₁₂ alkyl chain and from 1.8 to 9 ethylene oxide units.
 5. The functional fluid composition according to claim 1, wherein the alkoxy glycol borate ester comprises at least one an alkoxy glycol borate of formula (I) wherein n has a value of from 2 to
 4. 6. The functional fluid composition according to claim 1, wherein ) the alkoxy glycol borate ester comprises an alkoxy glycol borate of formula (I) wherein n has a value of 3 and R¹ is a methyl radical.
 7. The functional fluid composition according to claim 1, wherein the alkoxy glyocol component comprises a mixture of alkoxy glycols of formula (II) comprising solely or predominantly species with m=3.
 8. The functional fluid composition according to claim 1, wherein the composition exhibits a dry equilibrium reflux boiling point of at least 260° C., a wet equilibrium reflux boiling point of at least 180° C., or both.
 9. The functional fluid composition according to claim 1, wherein the composition exhibits a low temperature kinematic viscosity of less than 700 centistokes, determined at a temperature of −40° C.
 10. The functional fluid composition according to claim 1, wherein the composition is suitable as a brake fluid.
 11. The functional fluid composition according to claim 2, wherein the alkylamine ethoxylate comprises from 1 to 35 ethylene oxide units.
 12. The functional fluid composition according to claim 2, wherein the alkylamine ethoxylate comprises a linear C₇ to C₁₂ alkyl chain and from 1.8 to 9 ethylene oxide units.
 13. The functional fluid composition according to claim 3, wherein the alkylamine ethoxylate comprises a linear C₇ to C₁₂ alkyl chain and from 1.8 to 9 ethylene oxide units.
 14. The functional fluid composition according to claim 2, wherein the alkoxy glycol borate ester comprises an alkoxy glycol borate of formula (I) wherein n has a value of from 2 to
 4. 15. The functional fluid composition according to claim 3, wherein the alkoxy glycol borate ester comprises an alkoxy glycol borate of formula (I) wherein n has a value of from 2 to
 4. 16. The functional fluid composition according to claim 4, wherein the alkoxy glycol borate ester comprises an alkoxy glycol borate of formula (I) wherein n has a value of from 2 to
 4. 17. The functional fluid composition according to claim 2, wherein the alkoxy glycol borate ester comprises an alkoxy glycol borate of formula (I) wherein n has a value of 3 and R¹ is a methyl radical.
 18. The functional fluid composition according to claim 2, wherein the alkoxy glyocol component comprises a mixture of alkoxy glycols of formula (II) comprising solely or predominantly species with m=3.
 19. The functional fluid composition according to claim 2, wherein the composition exhibits a dry equilibrium reflux boiling point of at least 260° C., a wet equilibrium reflux boiling point of at least 180° C., or both.
 20. The functional fluid composition according to claim 2, wherein the composition exhibits a low temperature kinematic viscosity of less than 700 centistokes, determined at a temperature of −40° C. 